quarkusio/quarkus · error · IllegalArgumentException

Invalid template ${template}

Error message

Invalid template ${template}

What it means

URITemplate's constructor parses URI templates into path components. This IllegalArgumentException is thrown when a '{' segment containing a custom regex is malformed — e.g. a template like "{id:regex(...)}" whose inner expression does not match the expected custom-regex syntax, so the parser reaches an invalid state inside state 1.

Source

Thrown at independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/mapping/URITemplate.java:78

                        litChars++;
                        sb.append(c);
                    }
                    break;
                case 1:
                    if (c == '}') {
                        state = 0;
                        if (sb.length() > 0) {
                            capGroups++;
                            if (i + 1 == template.length() || template.charAt(i + 1) == '/') {
                                components
                                        .add(new TemplateComponent(Type.DEFAULT_REGEX, null, sb.toString().trim(), null, null,
                                                null));
                            } else {
                                components.add(new TemplateComponent(Type.CUSTOM_REGEX, "[^/]+?", sb.toString().trim(),
                                        null, null, null));
                            }
                        } else {
                            throw new IllegalArgumentException("Invalid template " + template);
                        }
                        sb.setLength(0);
                    } else if (c == ':') {
                        name = sb.toString().trim();
                        sb.setLength(0);
                        state = 2;
                    } else {
                        sb.append(c);
                    }
                    break;
                case 2:
                    if (c == '}' && bracesCount == 0) {
                        state = 0;
                        if (sb.length() > 0) {
                            capGroups++;
                            complexGroups++;
                            components
                                    .add(new TemplateComponent(Type.CUSTOM_REGEX, sb.toString().trim(), name, null,

View on GitHub (pinned to e1c734241f)

Solutions

1. Fix the template syntax inside braces; for custom regex use the form {name:regex("pattern")} or {name:pattern} supported by the parser
2. Escape or remove characters inside the braces that break parsing (unmatched parens/brackets)
3. Simplify to a plain parameter {name} if no custom pattern is needed
4. Test the template string in a unit test constructing new URITemplate(...) to fail fast

Example fix

// before
@Path("/items/{id:regex(")

// after
@Path("/items/{id:regex("\\d+")}")

// validate template before use
if (template.matches(".*\\{[^}]*:regex\\([^)]*$")) {
    throw new IllegalArgumentException("Malformed custom regex in template: " + template);
}

try {
    new URITemplate(template);
} catch (IllegalArgumentException e) {
    throw new IllegalArgumentException("Fix @Path on resource class: " + e.getMessage(), e);
}

When it happens

Trigger: Declaring a path parameter with an invalid custom regex form in a URI template, e.g. @Path("/items/{id:regex(") or an unrecognized special keyword after ':' inside braces that the parser cannot map to a TemplateComponent.

Common situations: Typos in custom regex declarations; copying templates from other frameworks (Spring/Spray syntax) unsupported here; unbalanced or unescaped regex characters inside braces; using unsupported syntax like {id: int} misspelled.

Related errors

• Invalid template ${template} Unmatched { braces
• Path not specified
• Name cannot start with '/':${name}
• Predicate already set
• Location already set

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/a4ec0678cfccad72. Report an issue: GitHub.